Any ideas what caused this?

[72buickgs]

[lun40119]

What were you doing when it happened?

[Orange65]

OUCH!

Broken piston could be detonation if it is cast, but it is hard to tell. The cylinder wall, IDK. What engine is it and any details of the failure (were you racing, did it just fail going down the road, had it been smoking, etc.)

[72buickgs]

455 Buick. Fresh build 10.5 compression aluminum pistons. Running down the road about 60 mph. Timing was set at 28 degrees AFR was 13.7. Had about 40 miles on it and hadn't got on it yet.

[TheSilverBuick]

Any chance the ring gap was too tight?

My first thought was perhaps water froze in the block, but that isn't likely on a fresh build given the time of year.

[lun40119]

That's what I was thinking...

[TheSilverBuick]

Was it overbored .060" or more? Any close up pictures of the lifter valley?

[Barry Donovan]

is it me or is there old grooves at the top of the wall. new stuff snapped at something discontent in its path...
and that is a big compression, going flat, it will slam walls even when they are good.

[MR P-BODY]

Thats a VERY large crack.... thin wall and porosity in the bore... I
will assume you didnt sonic check it before you worked on it

[TheSilverBuick]

I'd like to see the lifter bores to see if there is a sense of how much core shift is in the block. Also wonder if the chunk that popped up caused the piston to rock into the bore at TDC.

[72buickgs]

Bored 30 over. Temp was running @180. Machine shop put the bottom end together so I'm not sure on the ring gap. Would have to search through some paperwork.

[CDMBill]

Sorry for the bad news.

How long did it sit with water in the cylinder after the bad noises started? That dark ridge at the top says way rich, or the cylinder walls not prepped like one would expect.

[72buickgs]

It was running way rich when I first fired it. AFR was 9.3. Went down two full jets and one larger metering rod and had the AFR at 13.7 when it shit it's cookies. The block was sonic checked before anything was done. Russell, I didn't get any pictures of the lifter gallery and the block is back at the machine shop now.

[MR P-BODY]

It was running way rich when I first fired it. AFR was 9.3. Went down two full jets and one larger metering rod and had the AFR at 13.7 when it shit it's cookies. The block was sonic checked before anything was done. Russell, I didn't get any pictures of the lifter gallery and the block is back at the machine shop now.

What was the readings on the sonic check for that cyl

[greenXpress]

Sorry for the bad news.

How long did it sit with water in the cylinder after the bad noises started? That dark ridge at the top says way rich, or the cylinder walls not prepped like one would expect.

I go with cylinder wall not prepped right. But then I'm just an old tractor mechanic.